Adding collect function

- Collect function as fn:(collector, x) -> new_collector for collections
- Moving some definitions to "libs" folder
- Map and filter defined in mal

tests/arithmetic.mal

@@ -18,10 +18,6 @@
 (assert (= (/ -10 -2) 5))
 (assert (not (ok? (/ 12 0))))
 
-; mod
-(assert (= (mod 10 4) 2))
-(assert (= (mod 4 10) 4))
-
 ; >
 (assert (> 3 2))
 (assert (not (> 1 2)))
@@ -40,4 +36,4 @@
 ; <=
 (assert (<= 1 3))
 (assert (not (<= 3 2)))
-(assert (<= 1 1))
+(assert (<= 1 1))